Who cares?
Your questions bounce around like entries in an A-Z how to fly for beginners.... What started with an Original Post wrt Alpha Floor/Prot/Max very controversial in its understanding and being really well explained and expanded upon by other posters......
However, as is evident through other posts you make, questioning and seeking levels of clarification to diverse topics, you are angling to an agenda which may be through dare I suggest, what you have seen happen in your flight sim, game or whatever?
Any waypoint or level and speed constraint in the MCDU/FMGC is irrelevant to the topic you originally queried. If A/T is engaged it aims to maintain your speed with power....only if it no longer can for whatever reason will it lose the ability on thrust alone to maintain a selected or managed mode. Then Flight controls at that certain point, so well covered by Dupre and others, will lower the nose to maintain a speed commensurate and indicated by a combination of terms IE V and Alpha not necessarily the same values all the time.
Your last post talks about being in ALT selected or managed 2500Ft...... To me I read your alt is captured and maintained at 2500 FT it is only either selected or managed if you elect to change that with OP DES, DES, VS OR FPA .......ONLY THEN DOES IT BECOME SELECTED OR MANAGED.....I of course stand by to be corrected by the truly wise......(no sarcasm suggested there)